One of the approaches to the treatment of psoriasis is via the anti-proliferative& pro-differentiative activities of Vitamin D analogs or metabolites. The usefulness of this approach has been partially validated by the recent introduction by Bristol-Myers Squibb of calcipotriene, an effective topical treatment for psoriasis. Penederm Incorporated has recently acquired proprietary rights to 26,26,26,27,27,27-Hexafluoro-1-a,25-Dihydroxy Vitamin D3 which is being developed by Sumitomo Pharmaceutical Company, Ltd. as a systemic medication for osteoporosis and has potential for use as a psoriasis treatment. Due to the high potency of the compound, safety evaluation and formulation development require the use of high specific activity radiolabelled material which is not commercially available.